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New Member

Transcoding Clarification

I'm confused about some issues we've been having with transcoding.

We are using 7960's and 2600 H323 Gateways for PSTN Access. I also have a pair of 6608 blades for transcoding.

When Calls come into the H323 GW's from the PSTN the calls are G711. When the gateway passes the call to Call Manager the codec is negotiated based on the region the IP Phone is in. My 7960's are configured in a G729 region.

Now here is my confusion. Does the transcoder kick in and transcode the call from g711 to g729? Or does the H323 gateway do the transcoding?

Tim Medley

Cisco Employee

Re: Transcoding Clarification

The transcoder will only come into play if the other endpoint of the call (the 2600 in this case) is not configured to use G.729.

What you could do is configure a codec class on the 2600 to allow either G.711 or G.729 based on what the CallManager wants to use for each call, and then the transcoder would not be used.

New Member

Re: Transcoding Clarification


Yes I have a codec class configured on my 2600 gateway. So with this in mind, the gateway then takes the g711 stream from the PSTN (PRI) and transcodes it as g729 and directs the packets at the 7960 IP Phone using g729?

Then the only time my transcoder will kick in is when there is a device that doesn't support g729, such as my AS-8 gateway's to my voicemail system.


Tim Medley CCNP-Voice

Network Architect

VoIP Group


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